A compact low-supply-voltage yet low-noise digital bang–bang PLL (DBBPLL) is proposed. The bang–bang phase detector is based on a dynamic double-tail latch which enables high time-to-voltage gain and low input-referred noise under tight power-supply headroom. The ring-based digitally controlled oscillator (DCO) is made of multiple gm-controlled delay units and a constant-gm-biased current DAC. By combining these two blocks, the DCO can now better tolerate supply noise and process variations. A prototype DBBPLL has been implemented in a mainstream 28 nm CMOS process with a compact die area of 0.014 mm2. When operating at 2.6 GHz, it consumes 2.9 mW with 0.75 V supply and achieves low in-band phase noise of −105 dBc/Hz.